Student Kelsey Friend, becomes emotional while recounting her story about yesterday's mass shooting at the Marjory Stoneman Douglas High School where 17 people were killed. (Photo by Mark Wilson/Getty Images)

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Student Kelsey Friend, becomes emotional while recounting her story about yesterday's mass shooting at the Marjory Stoneman Douglas High School where 17 people were killed. (Photo by Mark Wilson/Getty Images)

In a matter of minutes, thousands of students at Marjory Stoneman Douglas High School went from thinking they were part of a fire drill to hiding inside closets and bathrooms to escape gunfire.

Authorities say Nikolas Cruz allegedly opened fire inside the Florida school on Wednesday, killing at least 17 people, both adults and children.

This is how events unfolded in one of the 10 deadliest mass shootings in modern U.S. history, according to law enforcement authorities, school officials and witnesses. All times are Eastern.

Wednesday, February 14

About 2:30 p.m.

• Cruz arrives at the Marjory Stoneman Douglas High School in Parkland, Florida. He is wearing a gas mask and carrying smoke grenades. It’s unclear if the smoke grenades were used.

• He allegedly sets off the school’s fire alarm, prompting the evacuation of some 3,000 students and staff. Investigators believe the suspect wanted to draw people out of classrooms to increase the number of casualties.

• The shooter uses a .223 caliber AR-15 firearm to carry out the massacre.

• As the school goes on lockdown, students take cover inside classrooms. Others jump over the school’s fences and escape to take shelter at a nearby Walmart. Some students text their loved ones and others post on social media images of chairs overturned in classrooms and floors stained with blood.

• Twelve people are killed inside the building, two outside and one in the street. Two others die at the hospital.

Hello, Twitter. I am closing my DM’s but I appreciate everyone contacting me. I am still locked in the school, but remember I’m only a freshman. Please don’t just send your love to me, but pray for the victims’ families too. Love you all.

• Authorities find Cruz in a nearby neighborhood and arrest him without incident. They identify him using school security videos.

• He is taken to the Broward Health North hospital because he has “labored breathing.” Cruz is treated and released to police custody.

4:20 p.m.

• Broward County Public Schools Superintendent Robert Runcie says the school received no warnings and that he was not aware of any threats against the school.

5:18 p.m.

• Florida Gov. Rick Scott travels to Broward County to be briefed about the shooting.

6 p.m.

• Authorities identify the alleged gunman as Nikolas Cruz, a 19-year-old former student at the high school. He arrives at the Broward County Sheriff’s Office wearing a hospital gown and is escorted inside by deputies.

6:30 p.m. to end of day

• School district officials say the school will remain closed for the rest of the week.

• The FBI sets up a website for students and others who were inside the school to upload videos and photos of the shooting.

• Law enforcement officials search Cruz’s home and another undisclosed location.

Thursday, February 15

• Cruz is expected to make his first court appearance in Broward County.